1. Field of the Invention
The present invention relates to a sheet feeding device and an image forming apparatus, and more particularly to a restricting member for restricting the end portion of sheets accommodated in a sheet storage portion.
2. Description of the Related Art
Conventionally, the image forming apparatus such as a copying machine, electrophotographic printer, ink jet printer, facsimile machine, printing machine is equipped with a sheet feeding device for feeding sheets one by one from a sheet storage portion which accommodates a plurality of sheets.
Generally, such a sheet feeding device feeds sheets stacked on a sheet stack tray by rotation friction of sheet feeding rollers whose surface is composed of rubber or the like. In this type, the feeding performance largely depends on friction coefficient of the surface of the sheet feeding roller. Therefore, there are disadvantages such as instability of sheet feeding performance due to changes in friction coefficient of the sheet feeding roller surface because of changes in external shape by friction of the feeding roller, changes of material with a time passage, adhesion of paper powder and the like and inability of meeting sheets having a different surface condition.
Recently, an air suction type sheet feeding device is proposed to convey sheets stacked on a sheet stack tray by suction force of air and feeding force of endless belt.
In this air suction type, air is blown against an end face of sheets stacked on the sheet stack tray with an air blowing means so as to form air layer between sheets, so that the sheet is floated thereby weakening adhesion force between the sheets. In the meantime, according to some air suction type, floating of the sheet accompanied by air blowing is restricted with a sheet pressing member at a specified position so as to allow air entering between the sheets to flow through, whereby weakening adhesion force between the sheets.
When air layer is formed between the sheet layers in this way, resistance between a floated sheet on a top layer and non-floated other sheet decreases. Thus, when the topmost sheet is fed with the feeding roller after it is conveyed by an endless belt by suction, a next sheet could be conveyed in an overlapping condition.
Thus, installation of a rear end pressing member which presses the rear end side of the stacked sheets from above is considered in order to prevent the next sheet from being conveyed in the overlapping condition. The technology of this rear end pressing member has been described in Japanese Patent Application Laid-Open No. 05-178483.
The rear end pressing member is sometimes provided on a rear end restricting member for restricting the rear end of the sheet in order to press the rear end portion of the sheet. This rear end restricting member needs to be moved along the end portion of the sheet by releasing fixing thereof each time corresponding to the size of stacked sheets when the size of the sheet is changed.
If sheets are stacked up to a height larger than the bottommost position of the rear end pressing member when the rear end restricting member is moved, unless the rear end pressing member is raised, the sheets could be set such that the front end of the rear end pressing member contacts an end face of the stacked sheets.
For example, when the rear end restricting member is changed to a position corresponding to a sheet of smaller size from a position corresponding to a sheet of a larger size, the rear end restricting member is often adjusted to the rear end of the sheets after the sheet stack is set. In this case, unless the rear end pressing member is raised, the sheets could be set in an erroneous condition in which the front end of the rear end pressing member butts against the end face of the sheet stack.
Consequently, the rear end pressing member does not make contact with the topmost sheet from above and thus the top layer sheet are not pressed and might be conveyed easily in an overlapping condition. Further, because the rear end restricting member does not contact the rear end face of sheets, the position of the sheet in a feeding direction may be dispersed, thereby causing a deviation of sheet feeding timing when the sheet is picked up.